Pipettes serve the dosing of liquids and are especially used in laboratories. Handheld and/or manually operational pipettes are of particular interest in connection with the invention. Such instruments comprise a sample container in which a (mostly liquid) sample to be drawn up is collected, and from which it can be dispensed again. The sample container is designed to be moved manually with the pipette, by hand in particular.
The collecting and the dispensing of a sample can be achieved, for example, by generating a negative pressure in the sample container to collect the sample, and an overpressure to dispense the sample. Piston pipettes, for example, possess a movable piston for that purpose, whereby an air column is arranged between the sample to be collected and the piston. During the movement of the piston into a first direction, the piston displaces the air column, while, during the movement into a second direction opposite a first direction, it pulls the air column and therefore also the sample to be collected into the sample container.
In order to prevent contamination, such pipettes may be provided with replaceable sample containers in the form of pipette tips. The pipette then comprises an interconnecting part that the pipette tip is pushed onto and from which it can be removed again after use. The pipette tip normally comprises two openings, whereby the interconnecting part is accommodated in the larger of the two openings during the attaching and seals it. The collecting and dispensing of the sample is done through the smaller opening. As only the pipette tip gets in contact with the sample to be collected, contamination with subsequent pipetting processes is prevented. The pipette tip is usually a disposable item made of plastic.
Besides purely mechanical pipettes, electronic pipettes also exist. Pipettes may also comprise one (with single-channel pipettes) or several (with multi-channel pipettes) interconnecting parts. Several interconnecting parts are furnished with a replaceable pipette tip to allow for the simultaneous collecting and dispensing of several samples. Depending on the quantity and attachment force used, the ejection of the pipette tips can require substantial strength. As the ejection mechanism of such pipettes is usually mechanical and operated by hand, this can result in fatigue of the hand during longer work cycles.
The ejection mechanisms used with handheld pipettes usually possess some similarities. This includes a slider that is configured to be movable along the interconnecting part. When operating the ejection mechanism, the slider is moved in the direction of the pipette tip, comes into contact with it and slides it off the interconnecting part. The ejection mechanism can be operated by means of an operating element. The operating element is usually operated by hand and is formed as a button, for example. The force exerted on the operating element can thereby be transferred to the slider mechanically and can thus effect its movement in the direction of the pipette tip. The part of the ejection mechanism that establishes the connection between the operating element and the slider can be designed in various ways, but generally comprises one or several movable links. The movement of the links is coupled with the movement of the slider. The links for the transfer of the force (when activating it) on the operating element are expediently formed on the slider.
The invention described in this document may also pertain to design variants of the previously described types of pipettes.